In recent years, as miniaturization of electronic devices has proceeded, it has been desired to increase the energy density of batteries, and various nonaqueous electrolyte batteries have been proposed.
For example, previously, metallic lithium has been used mainly for primary batteries as anodes for nonaqueous electrolyte batteries, and anodes of lithium alloys represented by aluminum/lithium alloys and carbon anodes have also been known.
However, when used as anodes for secondary batteries, metallic lithium has been known to be inferior in cycle stability due to formation of dendrites, etc.
Further, the anodes of the lithium alloys represented by the aluminum/lithium alloys do not extract full performance from the lithium batteries, although an improvement in cycle stability is observed compared with metallic lithium.
For solving such problems, it has also been proposed to use carbon anodes utilizing the fact that carbon intercalation compounds of lithium are electrochemically easily formed. Such carbon anodes include various ones. For example, a carbon material obtained by burning crystalline cellulose in a stream of a nitrogen gas at 1,800.degree. C. (Japanese Patent Unexamined Publication No. 3-176963), one obtained by graphitization treatment of coal pitch or petroleum pitch under an inert atmosphere at 2,500.degree. C. or more (Japanese Patent Unexamined Publication No. 2-82466) and one proceeding in graphitization treated at a high temperature exceeding 2,000.degree. C. are used, and provide anodes having a cycle stability, though a reduction in capacity is observed compared with metallic lithium and the lithium alloys. However for such anodes, a sufficient cycle stability has not been obtained in charge and discharge at a high current density.
When metallic lithium is used as the anodes of the lithium batteries, dendrites are formed upon charge and discharge. They not only cause deterioration, but also react with violence by contact with water, which raises the problem that the possibility of deterioration increases. Also, the lithium alloys are known not to be sufficient, although superior to metallic lithium in stability.
On the other hand, carbon anodes are sufficiently gentle in reaction with water also in the charged state, the state where lithium is intercalated in carbon, and the formation of dendrites upon charge and discharge is also barely observed. They are therefore excellent. However, many kinds of carbons can scarcely be charged and discharged, or are extremely low in capacity, compared with the theoretical capacity (assuming that the state of LiC.sub.6 is a maximum capacity).
Further, even if the initial capacity is relatively large, the capacity is deteriorated by repetition of charge and discharge. Even in the carbon anodes having a relatively large capacity, repetition of charge and discharge at a high current density provokes rapid deterioration, and the performance as secondary batteries can not be satisfied. Thus, anodes having adequate performance have not been obtained by the conventional carbon anodes.
Furthermore, for producing carbon for carbon electrodes, heat treatment at a high temperature of 2,000.degree. C. or more is necessary, and a method has been desired in which carbon can be produced at a lower temperature and more easily.
As is described above, carbon has come to be used as optimum electrode materials for secondary batteries, and can also be utilized for semiconductors, capacitors, activated carbon, etc. in addition, to widen its uses.
The present invention was carried out with the background of the conventional technical problems as described above, and an object is to provide a carbon material useful for an electrode material for a secondary battery, a capacitor, activated carbon, etc., particularly which has a high capacity, which is excellent in cycle stability, and which can also comply with charge and discharge at high current density; and a method for producing a carbon material in which such a carbon material can be obtained at a relatively low temperature (1,500.degree. C. or less) without heat treatment at a high temperature.